The present invention relates to a liquid ejection head and a method of manufacturing the same.
The liquid ejection head ejects pressurized liquid from a nozzle orifice as a liquid droplet, and the heads for various liquids have been known. An ink jet recording head is representative of the liquid ejection head. Here, the related art will be described with the ink jet recording head as an example.
An ink jet recording head (hereinafter, referred to as “recording head”) used as an example of a liquid ejection head is provided with a plurality of series of flow paths reaching nozzle orifices from a common ink reservoir via pressure generating chambers in correspondence with the orifices. Further, the respective pressure generating chambers need to form by a fine pitch in correspondence with a recording density to meet a request of downsizing. Therefore, a wall thickness of a partition wall for partitioning contiguous ones of the pressure generating chambers is extremely thinned. Further, an ink supply port for communicating the pressure generating chamber and the common ink reservoir is more narrowed than the pressure generating chamber in a flow path width thereof in order to use ink pressure at inside of the pressure generating chamber efficiently for ejection of ink drops. Further, it is important for normal discharge of ink droplets that ink supply ports that communicate with the pressure generating chambers and the nozzle orifices be formed correctly at prescribed positions of the pressure generating chambers.
To form the pressure generating chambers and the ink supply ports having such minute structures with high dimensional accuracy, very fine forging work is performed on a metal material plate (see Japanese Patent Publication No. 2000-263799A, for example).
As shown in FIG. 19, the pressure generating chambers are produced by forming a large number of elongated recess portions 71 in a metal material plate 70 and then performing finish working on the elongated recess portions 71. The elongated recess portions 71 are formed by pressing the material plate 70 between dies, that is, a first die 72 and a second die 73. In the first die 72, a large number of projections 74 for formation of the elongated recess portions 71 are arranged parallel with each other and gaps 76 for formation of partitions 75 of the pressure generating chambers are provided between the projections 74. Dummy projections 77 for formation of dummy recesses are located at end portions of the first die 72.
FIG. 18A shows the material plate 70 that has been subjected to the plastic working by the first die 72 and the second die 73.
The elongated recess portions 71 formed by the plastic working are arrayed to form a recess array. In a normal section 79 that is distant from the end of the recess array, the elongated recess portions 71 are formed with the prescribed length. However, in an abnormal section 80 in the vicinity of the end of the recess array, the length of the elongated recess portions 71 is getting shorter than the prescribed length toward the array end (a dummy recess 78). This situation is represented by a dimensional difference D between the end of the recess portion 71 in the normal section 79 and the end of the dummy recess portion 78 which is the shortest one.
There are several phenomena that are considered the causes of the above dimensional difference D. Among those phenomena, a special phenomenon relating to plastic flows occurring in the material plate 70 during plastic working would be the most influential factor. More specifically, in the normal section 79, when the projections 74 are dug into the material plate 70, plastic flows in the longitudinal direction of the projections 74 occur as intended while the flowing material goes into the gaps 76 to form sufficiently high partitions 75, because the adjoining projections 74 prevent plastic flows in the arrayed direction of the elongated recess portions 71. Therefore, the elongated recess portions 71 in the normal section 79 are given uniform lengths and their ends are aligned straightly.
On the other hand, in the abnormal section 80, since no elongated recess portion 71 exists outside the dummy recess portion 78, when the projection is dug into the portion of the material plate 70 that corresponds to the dummy recess portion 78, the material flows outward in the arrayed direction of the elongated recess portions 71 without being restricted. Because of this flow, the amount of material flowing in the longitudinal direction of the elongated recess portions 71 during the formation of the dummy recess portion 78 decreases, as a result of which the dummy recess portion 78 formed is shorter than the prescribed length. The above plastic flow in the arrayed direction of the elongated recess portions 71, which is permitted in forming the dummy recess portion 78, affects the formation of the elongated recess portion 71 next to the dummy recess portion 78 and the material also flows in the arrayed direction though the amount is smaller, as a result of which the elongated recess portion 71 formed is shorter than the prescribed length. Likewise, the material also flows in the arrayed direction in forming the elongated recess portion 71 that is second next to the dummy recess portion 78 though the amount is even smaller, as a result of which the elongated recess portion 71 formed is shorter than the prescribed length. This is a chain-reaction-like phenomenon. The degree of shortage in the length of the elongated recess portion 71 decreases as the position comes closer to the normal section 79, to form a smooth line connecting the ends of elongated recess portions 71 that are located around the boundary between the abnormal section 80 and the normal section 79. The dimensional difference D occurs as a result of the above phenomenon.
In summary, it is considered that the dimensional difference D is caused by the phenomenon that the plastic flows of material in the longitudinal direction of the elongated recess portions 71 in the abnormal section 80 are reduced by the occurrence of the plastic flows of material in the arrayed direction of the elongated recess portions, in particular, the occurrence of the plastic flow of material that is directed outward of the dummy recess portion 78.
Although not shown in FIG. 18A, an equivalent dimensional difference D may occur at both ends of the recess array.
Since short elongated recess portions 71 are formed as described above, the positions of the communicating ports that communicate with the pressure generating chambers and the nozzle orifices are not made uniform relative to the ends of the elongated recess portions 71. This results in various problems; for example, the working load of boring punches for forming the communicating ports becomes unduly heavy, ink is prevented from flowing smoothly to impair bubble ejection, and variations in the capacity and the shape of the pressure generating chambers cause an abnormality in the ink droplet discharge characteristics.
The most serious problem is that the working load of boring punches becomes unduly heavy. FIG. 18C shows a state that a communicating port 81 has been formed in an elongated recess portion 71 in the normal section 79. A first communicating port 81a having a large cross section and a closed bottom is formed by digging a boring punch through the middle or lower part of a slant face 82 at the end portion of the elongated recess portion 71. A second communicating port 81b is then formed by digging another boring punch into the bottom portion of the first communicating port 81a, whereby a two-step communicating port 81 is completed. A boring stroke S1 of the boring punch that is applied to the normal section 79 as in the above case is short and hence the working load of the boring punch is relatively light.
On the other hand, FIG. 18D shows a state that a communicating port 81 is formed in an elongated recess portion 71 in the abnormal section 80. Since the boring punches are aligned straightly, if the elongated recess portion 71 is shorter than the prescribed length by the dimensional difference D, a first communicating port 81a is formed at a position close to the top end of a slant face 82. Therefore, a boring stroke S2 is much longer than the boring stroke S1 so that strong lateral stress is exerted on the thin boring punch. As a result, the life of the boring punches to be applied to the abnormal section 80 is much shortened. And the frequency of breakage of the boring punches increases. Such shortening of the life causes a state that the punches cannot be used for the abnormal section 80 though they can well exercise the punching function for the normal section 79. This is uneconomical because the punches need to be replaced earlier. Further, frequent replacement of the punches lowers the productivity.
FIG. 18B shows a recess 83 that is formed so as to extend in the arrayed direction of the elongated recess portions 71. The recess 83 is provided to shape the end portions of the elongated recess portions 71 sharply and to keep the top surface of the material plate 70 flat. Without the recess 83, when the projections 74 of the first die 72 are dug into the material plate 70, the material that flows in the longitudinal direction of the elongated recess portions 71 would form a rise as indicated by dashed chain lines in this figure. Such a rise exerts reaction force on the end portions of the projections 74 being dug, as a result of which the end portions of the elongated recess portions 71 are not formed sharply. Further, the rise would lower the flatness of the top surface of the chamber formation plate. The formation of the recess 83 solves the above problems because it absorbs the material flowing thereinto that would otherwise form the rise.